The invention relates to a system comprising a plurality of apparatuses for processing user information signals, each apparatus having an interface for the communication of control messages via a serial data channel and being independently addressable via said data channel bus, the apparatuses including:
at least one first apparatus having at least one output connector for a given class of user information signal; and PA1 at least one second apparatus having at least one input connector for the given class of user information signal, the input connector being connectable via a cable to the output connector of the first apparatus; PA1 means addressable via the data channel as a control subdevice for generating a sequence of control messages for controlling said automatic determination, said sequence including first, second and third types of messages; PA1 signal generator means within each first apparatus for (i) in response to a message of the first type interrupting the supply of user information signals of the given class to the output connector(s) of the first apparatus, (ii) in response to a subsequent message of the second type selectively enabling the supply of such signals to just one output connector of the first apparatus, and (iii) in response to a message of the third type re-enabling the supply of such signals to the output connector(s) of the first apparatus to allow normal operation thereof; and PA1 detection means connectable to the or each said input connector of the second apparatus for indicating to the control subdevice whether a user-information signal of the given class is being received at that connector.
the system including cable detection means for determining automatically which first apparatus, if any, is connected to the or each input connector of the second apparatus.
The invention further relates to apparatuses suitable for use as the first and/or second apparatus in such a system.
A system as set forth in the opening paragraph has been described in European Patent Application EP-A1-0 257 684 (PHN 11838). The system uses the serial data channel to enable automated detection of connecting cables between certain domestic video entertainment apparatuses and a switching device. Such automation is desirable in view of the increasing complexity of such systems, which should be hidden from the human user as far as possible. For the serial data channel, the system proposed in EP-A1-0 257 684 makes use of the Domestic Digital Bus (D2B) as standardized by the International Electrotechnical Commission (IEC), Geneva, published in their document number 1030 and previously available in draft form. Of course other wired or wireless data channels could be envisaged for the communication of control messages.
The system of EP-A1-0 257 684 exploits the widespread adoption of multi-wire cabling in domestic audio/video systems, based on the Euroconnector (SCART) standard, and uses certain conductors, additional to those which carry the user information signals (video signals in the example), to pass signals for the purpose of automatic cable detection. Once the network of interconnections has been identified control messages can be used to establish specific signal paths automatically to implement a user's desired function, for example as described in GB-A-2 223 114 (PHN 12678).
Unfortunately, the reliance of the proposed system on additional conductors necessitates an additional cost in the construction of apparatuses and cables for use in the system, by requiring special signal generating and detecting hardware which might not otherwise be required. Audio equipment in particular does not normally employ multi-wire cabling at all.